1. Field of the Invention
The present invention relates to an simulated engine characteristic control system for power train performance tests for automotive vehicles, particularly to a system utilized for transient performance tests for automotive transmissions, for example an endurance test for synchronizing devices used in manual transmissions, wherein a test is made to simulate stress applied to the synchronizing devices when shifting during high acceleration or quick deceleration, and a feeling test for automatic transmissions, wherein a test is made to determine whether or not shifting is smoothly executed during simulated acceleration and/or deceleration. Specifically to a system in which transient performance tests for transmissions can be simulated by replacing the internal combustion engine associated with a transmission to be tested with a direct-current (DC) motor serving as a driving device.
2. Description of the Prior Art
Conventionally, there have been proposed and developed various transient performance test machines for automotive vehicles. In transmission performance tests, the engine associated with the transmission being tested is in general utilized as a driving device for the tested transmission. In this situation, many ancillary facilities are necessitated to operate the engine, thereby resulting in a relatively large test space. Furthermore, the horsepower generated from the engine may vary slightly due to changes in the ambient temperature during the performance test. For this reason, it was desirable that the engine drive method be replaced with a motor drive method. As is generally known, since an axial moment of inertia of the rotor employed in the motor is much greater than that of the rotating member of the engine, such as an engine crankshaft and a flywheel, such motor drive devices cannot sufficiently simulate changes in engine speed due to the low responsiveness of such devices when compared to an engine. Therefore, recently, there has been proposed and developed a transmission transient performance test machine including a relatively low inertia motor drive device which can generate output revolutions and output torques similar to an engine which operates in combination with a speed-increasing gear so as to have an axial moment of inertia similar to the rotating member of an engine. This low inertia of the rotor of the DC motor is accomplished by a highly rigid rotating shaft and a cooling device being capable of efficiently cooling the motor. One such conventional transmission transient performance test machine is shown in FIG. 1. Referring now to FIG. 1, the input shaft of a tested transmission 1 is connected through a torquemeter 8 to a low inertia DC motor 2 including a speed-increasing gear, while the output shaft of the transmission 1 is connected to a dynamometer 3 serving as a load applied to the transmission 1. Reference numeral 4 denotes an engine characteristic generator which generates a torque command signal T.sup.* in accordance with an engine revolution/torque characteristic map being comprised of a plurality of engine revolution/torque characteristic curves depending on the respective opening angle of the throttle valve of the engine. The map is assumed and preset in the engine characteristic generator 4, on the basis of the characteristics associated with the engine normally coupled with the tested transmission. The engine characteristic generator 4 is connected to a throttle opening angle signal generator (not shown) or an intake manifold pressure signal generator (not shown) and generates a torque command signal to a torque controller 7, in response to either a throttle opening angle signal .theta. from the above mentioned throttle opening angle signal generator or an intake manifold pressure signal from the above mentioned intake manifold pressure signal generator. The engine characteristic generator 4 also receives an actual revolution signal N through a pulse pick-up 5, disposed in the vicinity of the rotating shaft of the DC motor 2 for detecting actual revolution of the DC motor 2, and a frequency/voltage transducer 6, processing pulses from the pulse pick-up 5 to a voltage signal indicative of the actual rpm of the DC motor 2. For instance, when the engine characteristic generator 4 receives the signal .theta..sub.i indicative of a throttle opening angle of 100%, the generator 4 generates the torque command signal T.sup.* determined according to the actual revolution N of the DC motor 2, plotted on the uppermost curve shown in FIG. 1, indicating the engine revolution/torque relationship at a full throttle state. Conversely, when the engine characteristic generator 4 receives the signal .theta..sub.o indicative of a throttle opening angle of 0%, the generator 4 outputs the torque command signal T.sup.* determined according to the actual revolution N, plotted on the lowermost curve shown in FIG. 1, indicating the revolution/torque relationship at a fully closed throttle valve state. In the engine characteristic generator 4 as shown in FIG. 1, although the two engine revolution/torque curves are indicated between the uppermost and lowermost curves, more engine revolution/torque curves may be stored in the generator 4, depending on throttle opening angles of the engine. For instance, ten engine revolution/torque curves may be selected according to step-by-step throttle opening angles. The torque controller 7 compares the torque command signal T.sup.* from the engine characteristic generator 4 and the detected output torque signal T from the previously described torquemeter 8, and thereafter controls the DC motor 2 in such a manner as to reach the detected output torque T to the torque command signal T.sup.*. In other words, the input torque applied to the tested transmission 1 is adjusted by the feedback control on the basis of the torque output from the DC motor 2. In this manner, in conventional transmission transient performance test machines, the torquemeter detects the actual output torque T from the DC motor and thereafter the detected torque T is controlled in a manner so as to reach the command torque T.sup.* by feedback control, thereby permitting high accuracy of the output torque T. However, the responsiveness of conventional test machines is relatively low, for example 1 to 3 sec due to delay of the feedback control with regard to the output torque from the DC motor. Such conventional test machines may not satisfactorily respond to the previously described transmission transient performance tests.
In order to improve the responsiveness of the torque control, there has been proposed and developed another type transmission transient performance test machine wherein output torque from a DC motor for driving a tested transmission is derived from an actual current or voltage applied to the DC motor. In this case, since the output torque from the DC motor is not determined by a torque signal from a torquemeter disposed in the output side of the DC motor but by a current or voltage applied to the input side of the DC motor, the responsiveness of the test machine is improved. However, when comparing the previously described two conventional transmission transient performance test machines, the latter is inferior to the former with regard to the accuracy of the output torque control of the DC motor.